This is a revised R29 application that seeks to employ the oim/oim mouse as a model for osteogenesis imperfecta (OI) and dentinogenesis imperfecta. Of central interest will be alterations at the mineral-matrix interface. The first aim is to assess the validity of the model, specifically focusing on the mineral-matrix interactions. Secondly, the effect of altered collagen structure on mineral formation as opposed to resorption and turnover will be assessed by comparing mineral abnormalities in dentin and bones of the oim/oim mouse. Third, the relative contributions of impaired collagen and impaired mineral to altered bone stiffness will be determined. The fourth aim will test the effects of a third generation bisphosphonate that is postulated to have on increasing mechanical strength of bones in growing oim/oim mice.